Silicone pressure sensitive adhesive compositions

Abstract

 This invention provides pressure sensitive adhesive compositions which are obtainable by a method comprising reacting a mixture comprising at least one polydiorganosiloxane, at least one silicone resin copolymer, at least one solvent or plasticizer selected carboxylic acids having at least six carbon atoms and having a boiling point of at least 200°C. or amines having at least 9 carbon atoms and having a boiling point of at least 200°C. to form a reaction product, and then adding an organic peroxide or azo compound to the resultant reaction product. The silicone pressure sensitive adhesives of this invention are useful in preparing articles such as pressure sensitive tapes, labels, emblems and other decorative or informational signs.

Description

[0001] This invention provides silicone pressure sensitive adhesive compositions obtainable by reacting a mixture comprising a polydiorganosiloxane, a silicone resin copolymer and at least one solvent or plasticizer selected carboxylic acids having at least six carbon atoms and having a boiling point of at least 200°C. or amines having at least 9 carbon atoms and having a boiling point of at least 200°C. to form a reaction product and then adding an organic peroxide or azo compound to the reaction product.

[0002] Silicone pressure sensitive adhesives (PSA's) are typically produced by either blending or condensing together a silicone resin and a silicone polymer. These types of silicone pressure sensitive adhesives are claimed in U.S. Patent Nos. 2,736,721, 2,814,601, 2,857,356 and 3,528,940.

[0003] Silicone pressure sensitive adhesives which are produced by adding an amine or a salt of an amine to the silicone resin-silicone polymer blend are disclosed in Great Britain Patent Publication 998,232. Silicone pressure sensitive adhesives are also disclosed which comprise a resin, a polydiorganosiloxane fluid and a condensation catalyst such as a metal salt of a carboxylic acid in U.S. Patent 4,831,070.

[0004] European Patent Application 0459292 provides a silicone pressure sensitive adhesive composition comprising a mixture of two different pressure sensitive adhesive compositions containing resin and polymer blends.

[0005] U.S. Patent 5,248,739 teaches a silicone pressure sensitive adhesive composition produced by mixing together a silicone resin and a polydiorganosiloxane polymer and that these compositions can further comprise an organic peroxide as a crosslinking agent when the polydiorganosiloxane polymer does not contain unsaturated groups.

[0006] Great Britain Patent Publication 2,301,829 discloses silicone pressure sensitive adhesive compositions comprising 100 parts of an organopolysiloxane having a viscosity of at least 500,000 mPa·s(cP) at 25°C., 60 to 300 parts of a silicone MQ resin, and 20 to 2500 parts of a linear or cyclic volatile organosiloxane fluid having a boiling point in the range of 95 to 250°C. where the organo radicals of the silicone pressure sensitive adhesive composition are selected from C_1-13 organo radicals which are attached to silicon by carbon-silicon linkages. This publication further discloses the curing of the silicone composition with a free-radical initiator such as an organic peroxide.

[0007] Conventional peroxide curable silicone pressure sensitive adhesives are generally supplied at 55 to 60% solids by weight in an organic (typically aromatic) solvent diluent. This is done to lower the viscosity of the film forming product, making it easier to handle and apply evenly to a desired substrate.

[0008] We have found the addition of certain high boiling point solvents or plasticizers to silicone pressure sensitive adhesive compositions can improve the performance of the adhesive and eliminate the need for a separate silanol condensation catalyst.

[0009] Our invention claims silicone pressure sensitive adhesive compositions which are obtained by reacting a mixture comprising at least one polydiorganosiloxane, at least one silicone resin copolymer, and at least one solvent or plasticizer selected from carboxylic acids having at least six carbon atoms and having a boiling point of at least 200°C. or amines having at least 9 carbon atoms and having a boiling point of at least 200°C. to form a reaction product, and then adding an organic peroxide or azo compound to the reaction product.

[0010] Silicone pressure sensitive adhesive compositions produced by our invention exhibit high tack while retaining good peel adhesion.

[0011] It is an object of our invention to provide a silicone pressure sensitive adhesive compositions that are produced without the need for a separate silanol condensation catalyst.

[0012] It is further an object of this invention to provide a silicone pressure sensitive adhesive compositions having high solids content which maintain excellent adhesive properties at low viscosities.

[0013] It is another object of this invention to provide a silicone pressure sensitive adhesive compositions which are particularly suitable in adhesive tape constructions.

[0014] Our invention introduces a silicone pressure sensitive adhesive composition obtainable by a method comprising the steps of (I) reacting a mixture comprising: (A)(i) at least one hydroxyl-terminated polydiorganosiloxane having a viscosity of from 100 to 100,000,000 mm²/s at 25°C. or (ii) a mixture of (a) a hydroxyl-terminated polydiorganosiloxane and (b) a polydiorganosiloxane selected from (i) polydiorganosiloxanes terminated with monovalent hydrocarbon radicals free of aliphatic unsaturation or (ii) alkenyl-terminated polydiorganosiloxanes wherein said mixture has a viscosity of from 100 to 100,000,000 mm²/s at 25°C., (B) at least one soluble silicone resin essentially consisting of at least one R₃SiO_1/2 unit and at least one SiO_4/2 unit, wherein R is independently selected from a monovalent hydrocarbon or halohydrocarbon radical free of aliphatic unsaturation and having from 1 to 20 carbon atoms, an alkenyl radical, or a hydroxyl radical wherein the molar ratio of R₃SiO_1/2 units to SiO_4/2 units is from 0.5:1 to 1.2:1, and (C) at least one solvent or plasticizer selected from carboxylic acids having at least six carbon atoms and having a boiling point of at least 200°C. or amines having at least 9 carbon atoms and having a boiling point of at least 200°C. to form a reaction product, and (II) adding (D) an organic peroxide or azo compound to the reaction product of (I).

[0015] The hydroxyl-terminated polydiorganosiloxane of component (A) is a polydiorganosiloxane having the general formula HOR¹₂SiO(R¹₂SiO)_aSiR¹₂OH wherein each R¹ is independently selected from a monovalent hydrocarbon or halohydrocarbon radical having from 1 to 20 carbon atoms or an alkenyl radical. The monovalent hydrocarbon radicals free of aliphatic unsaturation include alkyl radicals exemplified by methyl, ethyl, propyl, pentyl, octyl, undecyl or octadecyl; cycloaliphatic radicals exemplified by cyclohexyl; aryl radicals exemplified by phenyl, tolyl, xylyl, benzyl or 2-phenylethyl; and chlorinated hydrocarbon radicals exemplified by 3-chloropropyl and dichlorophenyl. The alkenyl radicals include vinyl, allyl, butenyl, hexenyl, cyclohexenyl and beta-cyclohexenylethyl. Preferably, R¹ is selected from methyl, phenyl or vinyl. The most preferred hydroxyl-terminated polydiorganosiloxane of component (A) is a compound in which at least 50%of the R¹ radicals are methyl radicals.

[0016] The average value of subscript "a" above provides a viscosity at 25°C. of 100 mm²/s (100 cS) to 100,000,000 mm²/s (100,000,000 cS), the viscosity is a function of the R¹ radicals on the polymer. A preferred average value of

a" provides an organopolysiloxane component (A) having a viscosity in the range of 1,000 to 50,000,000 mm²/s at 25°C. More is when

a" has a value such that the viscosity of component (A) ranges from 2,000 to 500,000 mm²/s at 25°C.

[0017] Specific examples of these polydiorganosiloxanes include; HOMe₂SiO(Me₂SiO)_aSiMe₂OH, HOMe₂SiO(Me₂SiO)_0.94a(Ph₂SiO)_0.06aSiMe₂OH, HOPh₂SiO(Me₂SiO)_0.94a(Ph₂SiO)_0.06aSiPh₂OH, HOMe₂SiO(Me₂SiO)_0.95a(MeViSiO)_0.05aSiMe₂OH, HOVi₂SiO(Me₂SiO)_0.95a(MeViSiO)_0.05aSiVi₂OH or HOR₂SiO(Me₂SiO)_0.88a(Ph₂SiO)_0.12aSiR₂OH wherein Me, Vi and Ph hereinafter denote methyl, vinyl and phenyl, respectively, and

a" is as defined above. Component (i) can also be a mixture of two or more different hydroxyl-terminated polydiorganosiloxanes.

[0018] Component (A) can also be (ii) a mixture of (a) a hydroxyl-terminated polydiorganosiloxane and (b) a polydiorganosiloxane selected from (i) polydiorganosiloxanes terminated with monovalent hydrocarbon radicals free of aliphatic unsaturation or (ii) alkenyl-terminated polydiorganosiloxanes wherein said mixture has a viscosity of from 100 to 100,000,000 mm²/s at 25°C. The hydroxyl-terminated polydiorganosiloxane is as above including preferred embodiments thereof. The monovalent hydrocarbon radicals free of aliphatic unsaturation and the alkenyl radicals are as above including preferred embodiments thereof.

[0019] Specific examples of polydiorganosiloxanes terminated with monovalent hydrocarbon radicals free of aliphatic unsaturation include;Me₃SiO(Me₂SiO)_aSiMe₃, Me₃SiO(Me₂SiO)_0.95a(MeViSiO)_0.05aSiMe₃, Me₃SiO(Me₂SiO)_0.5a(MePhSiO)_0.5aSiMe₃ or Me₃SiO(Me₂SiO)_0.5a(Ph₂SiO)_0.5aSiMe₃ wherein

a" has an average value as defined above.

[0020] Specific examples of polydiorganosiloxanes terminated with alkenyl radicals include; ViMe₂SiO(Me₂SiO)_aSiMe₂Vi, ViMe₂SiO(Me₂SiO)_0.95a(MePhSiO)_0.05aSiMe₂Vi, ViMe₂SiO(Me₂SiO)_0.98a(MeViSiO)_0.02aSiMe₂Vi, PhMeViSiO(Me₂SiO)_aSiPhMeVi, ViMe₂SiO(Me₂SiO)_0.95a(Ph2SiO)_0.05aSiMe₂Vi and PhMeViSiO(Me₂SiO)_0.8a(MePhSiO)_0.1a(Ph₂SiO)_0.1aSiPhMeVi wherein a has an average value as defined above.

[0021] If component (A) is (ii) a mixture of (a) and (b) as defined above, the mixture of (a) and (b) is in weight ratios of (a):(b) of 1:99 to 99:1, is preferably from 90:10 to 10:90, and more preferred is from 70:30 to 30:70.

[0022] In component (A) the molar sum of phenyl and vinyl radicals cannot exceed 30% of the silicon atoms. In addition, component (A) can comprise trace amounts of siloxane branching sites; namely, R¹SiO_3/2 units and SiO_4/2 units, provided that the component remains flowable. Component (A) is well known in the art and is prepared by known methods which need not be repeated herein.

[0023] The amount of component (A) in our compositions is from 30 to 50 parts by weight and, more preferably, from 37 to 47 parts by weight per 100 parts by weight of components (A)+(B).

[0024] Component (B)is at least one soluble silicone resin essentially consisting of at least one R₃SiO_1/2 unit (M unit) and at least one SiO_4/2 unit (Q unit), wherein R is independently selected from a monovalent hydrocarbon or halohydrocarbon radical having 1 to 20 carbon atoms, an alkenyl radical or a hydroxyl group, all of which are as described above. The term "soluble" means the silicone resin (B) is dispersed in either a hydrocarbon liquid exemplified by benzene, toluene, xylene, heptane and the like or in a silicone liquid such as cyclic or linear polydiorganosiloxanes. The resin is soluble in component (A), delineated hereinabove. The silicone resin of component (B) is a soluble hydroxy-functional organopolysiloxane resin consisting of M units and Q units. In the hydroxyl functional organopolysiloxane resin, the R₃SiO_1/2 units are bonded to the SiO_4/2 units, each of the latter being bonded to at least one other SiO_4/2 unit. Some of the SiO_4/2 units are bonded to hydroxy radicals resulting in HOSiO_3/2 units, thereby accounting for the silicon-bonded hydroxyl content of the resin. In addition, the resin may contain a small amount of a low molecular weight material comprised of a neopentamer organopolysiloxane having the formula (R₃SiO)₄Si.

[0025] The preferred hydroxy-content of the silicone resin or resin mixture as determined by ²⁹Si NMR (nuclear magnetic resonance) ranges from 1.0 to 5.0 wt% based on the resin solids content, and preferably 1.5 to 3.5 wt%. However, resins having less than 1.0 wt% hydroxy can also be used in this invention.

[0026] In the formula for organopolysiloxane resin (B), the monovalent hydrocarbon radicals free of aliphatic unsaturation and the alkenyl radicals are as defined above, including preferred embodiments thereof. R is independently selected from methyl, phenyl, vinyl or hydroxyl. At least one-third and, more preferably, all R radicals in the formula for component (B) are methyl radicals. Examples of preferred R₃SiO_1/2 units include Me₃SiO_1/2, ViMe₂SiO_1/2, PhMe₂SiO_1/2 or Ph₂MeSiO_1/2.

[0027] The molar ratio of R₃SiO_1/2 units to SiO_4/2 units is 0.5:1 to 1.2:1. A molar ratio of the R₃SiO_1/2 units to SiO_4/2 units between 0.6:1 and 1:1 is preferred. The M:Q molar ratios are determined by ²⁹Si NMR. A number average molecular weight (Mn) of 3,000 to 7,500 for component (B) is preferred as measured by gel permeation chromatography (GPC) calibrated against fractionated MQ resin standards. A molecular weight (Mn) of Component (B) from 3,500 to 6,000 is most preferred.

[0028] Component (B) is prepared by by the silica hydrosol capping process of U.S. Patent 2,676,182, as modified by U.S. Patent 3,627,851 and U.S. Patent 3,772,247, wherein each patent teaches how to prepare soluble organopolysiloxanes that are useful in this invention. Further, component (B) is obtainable by the cohydrolysis of a trialkyl hydrolyzable silane and alkyl silicate as described in U.S. Patent 2,857,356.

[0029] The amount of component (B) in the compositions of our invention is from 50 to 70 parts by weight and, more preferably, from 53 to 63 parts by weight per 100 parts by weight of components (A)+(B). A preferred embodiment is the addition of a separate high-resin containing polymer-resin mixture to the initial resin-polymer mixture such that the resin content of the proportion of the combined resin and polymer mixture is within the above limits.

[0030] Component (C) is at least one solvent or plasticizer selected from carboxylic acids having at least six carbon atoms and having a boiling point of at least 200°C. or amines having at least 9 carbon atoms and having a boiling point of at least 200°C. The term "boiling point" denotes the boiling point of a liquid at standard atmospheric pressure (101.3 kPa). The carboxylic acids are exemplified by nonanoic acid, caproic acid, caprylic acid, oleic acid, linoleic acid, linolenic acid and N-coco-beta-aminobutyric acid. The amines are exemplified by dodecylamine, hexadecylamine, octadecylamine, dimethyldodecylamine, dicocoamine, methyldicocoamine, dimethyl cocoamine, dimethyltetradecylamine, dimethylhexadecylamine, dimethyloctadecylamine, dimethyl tallow amine, dimethylsoyaamine, dimethyl nonylamine, di(hydrogenated-tallow)amine and methyldi(hydrogenated-tallow)amine. Component (C) can also be a combination of two or more different carboxylic acids as above, a combination of two or more different amines as above or a combination of a carboxylic acid as above and an amine as above. The materials of component (C) are a catalyst and solvent in the silicone pressure sensitive adhesive compositions of this invention (i.e. dual functional). This feature eliminates the need for using a silanol condensation catalyst.

[0031] Amine or carboxylic acid of component (C) have a boiling point of at least 210°C. are preferred and, more preferred, are amines or carboxylic acids having a boiling point of at least 225°C. Preferably, component (C) is miscible in components (A) and (B). Miscible denotes that Component (C) has the ability to dissolve uniformly in the mixture of (A)+(B).

[0032] The amount of component (C) used depends on the type of amine or carboxylic acid selected. If an amine or carboxylic acid having a boiling point near 200°C. is selected, a greater amount of amine or carboxylic acid is required. The amount of component (C) in the compositions of our invention is preferably from 2 to 40 parts by weight and, more preferable, from 5 to 30 parts by weight per 100 parts by weight of components (A)+(B).

[0033] The mixture of step (I) can further comprise (E) at least one solvent or plasticizer having a boiling point of at least 200°C. selected from the group consisting of aliphatic hydrocarbons, glycol ethers, esters, alcohols, ester alcohols, ketones, kerosenes, naphthas and petrolatums. The aliphatic hydrocarbons are exemplified by dodecane (boiling point (bp) of 216°C.), tridecane (bp of 234°C.), tetradecane (bp of 252°C.), 1-tetradecene (bp of 256°C.), pentadecane (bp of 266°C.), hexadecane (bp of 280°C.), octadecane (bp of 308°C.) and nonadecane (bp of 320°C.). The glycol ethers are exemplified by diethylene glycol ethyl ether (bp of 202°C.), diethylene glycol butyl ether (bp of 230°C.), triethylene glycol methyl ether (bp of 242°C.), triethylene glycol ethyl ether (bp of 254°C.), triethylene glycol butyl ether (bp of 283°C.), ethylene glycol phenyl ether (bp of 245°C.), propylene glycol phenyl ether (bp of 243°C.), and aromatic based glycol ethers (bp of 245°C.). The esters are exemplified by diethylene glycol butyl ether acetate (bp of at least 235°C.), pine oil (bp of at least 212°C.), and mineral seal oil (bp of at least 278°C.). The alcohols are exemplified by tridecyl alcohol (bp of 252°C.), and the ester alcohols are exemplified by trimethyl pentane diol isobutyrate (bp of at least 244°C.). The ketones exemplified by isophorone (bp of at least 215°C.). It is preferred that component (E), if present, is miscible in components (A) and (B). Miscible denotes that Component (E) has the ability to dissolve uniformly in the mixture of (A)+(B).

[0034] The amount of component (E) used is dependent on the type of solvent or plasticizer selected. If component (E) has a boiling point near 200°C., a greater amount of solvent or plasticizer is required. The amount of component (E) in the compositions of this invention is from 2 parts by weight to 40 parts by weight and, more preferred, from 5 parts by weight to 30 parts by weight per 100 parts by weight of components (A)+(B).

[0035] The mixture of step (I) can also comprise a rare earth metal salt of a fatty acid. Examples of rare earth metals suitable for forming the salt include cerium, lanthanum, praseodymium, with cerium the most preferred. The fatty acid contains 6 to 18 carbon atoms, most preferably, 8 carbon atoms. The preferred rare earth metal salt is cerium octoate. Rare earth metal salt concentration in our compositions are within the range of from 1 to 1000 parts by weight, and most preferred from 10 to 250 parts by weight per one million parts by weight of components (A)+(B). Typically, the rare earth metal salt when used is in the form of a 30% solvent solution, 6% of which is composed of the active rare earth metal. Solvents suitable for the rare earth metal solution are solvents having a boiling point of less than 200°C. such as hexane, heptane, toluene, xylene, naphtha, mineral spirits or ketones.

[0036] The reaction product of step (I) is made by reacting a mixture of components (A), (B) and (C). Reacting for the purposes of this invention denotes simply mixing components (A), (B) and (C); and any optional components at room temperature (25°C.) or heating a mixture of components (A)-(C) and any optional components at temperatures above room temperature. A mixture of components (A)-(C) and any optional components are heated at a temperature above 100°C. A preferred embodiment of the reaction process is to pre-neutralize catalytic impurities which are often introduced with the raw materials of the adhesive product. The mixing of these components is enhanced with the use of one or more solvents having a boiling point of less than 200°C. in the mixture of step (I), such as benzene, toluene, xylene, naphtha, mineral spirits, cyclic polysiloxanes or alcohols such as methanol, ethanol, isopropanol, butanol or n-propanol. The amount of solvent having a boiling point of less than 200°C., if used, ranges from 60 to 200 parts by weight per 100 parts by weight of components (A)+(B). The mixture of (A)-(C) is heated for 4 hours at temperatures of from 100 to 180°C., however, the time and temperature are dependent on the selection and concentration of the reaction components. The reaction is complete when the viscosity of the reaction product remains constant or decreases after achieving a maximum value. The reacting of the mixture of (A)-(C) results in the formation of a reaction product.

[0037] When a solvent having a boiling point of less than 200°C. is used, it is necessary to remove this solvent after the formation of the reaction product. Methods of removing volatile components are well known in the art and need not be repeated herein. Any method of removing volatile components can be used, such methods exemplified by molecular stills, rotoevaporators and wipe film evaporators, with the preferred method being rotoevaporators.

[0038] It is preferred that the reaction product of step (I) have a solids content of at least 60% and a viscosity of up to 200,000 (mPa·s), a solids content of at least 75% is more preferable with a viscosity of up to 150,000 mPa·s. Most preferred is when the reaction product of step (I) has a solids content of at least 80% and a viscosity of up to 100,000 mPa·s.

[0039] In step (II), component (D) an organic peroxide or azo compound is added to the reaction product of step (I). Examples of preferred organic peroxides which are suitable as component (D) include diacyl peroxides such as benzoyl peroxide or dichlorobenzoyl peroxide. Benzoyl peroxide is a particularly effective organic peroxide.

[0040] Examples of azo compounds suitable as component (D) include azobenzene, azobenzene-p-sulfonic acid, 2,4-dimethyl-4-methoxyvaleronitrile, azobisdimethylvaleronitrile, azobisisobutyronitrile or azodine, with azobisisobutyronitrile being preferred. Component (D) when added to the product of step (I) is a solution in a solvent having a boiling point of less than 200°C., namely, benzene, toluene, xylene, naphtha, chlorocarbons, ketones or mineral spirits.

[0041] The amount of Component (D) in the compositions of this invention is from 0.1 to 5 parts by weight and, more preferably, from 1.5 to 3.5 parts by weight per 100 parts by weight of components (A)+(B).

[0042] During or after the formation of the silicone pressure sensitive adhesive composition, small amounts of additional ingredients may be added to the composition providing they do not materially affect the pressure sensitive adhesive composition. These additional ingredients are exemplified by, but not limited to, antioxidants, pigments, stabilizers and fillers. It is apparent that a blend of two or more reaction products, each having different amounts of components (A), (B) and (C), is formed in Step (I), and the blend is catalyzed according to Step (II). Our invention further provides articles of manufacture prepared by (I) applying a silicone pressure sensitive adhesive composition to at least one surface of a substrate, wherein the silicone pressure sensitive adhesive composition is the above described silicone pressure sensitive adhesive composition and (II) heating the silicone pressure sensitive adhesive composition and the substrate to cure the composition. The method can further comprise (III) contacting a solid support with the substrate having the adhesive composition cured thereon after step (II) whereby the solid support and the substrate are adhered together.

[0043] The silicone pressure sensitive adhesive compositions of this invention are useful to adhere a substrate to a solid support, whether flexible or rigid. These compositions may be applied to a surface of a substrate by any suitable means namely rolling, spreading or spraying and cured as described above.

[0044] The surface of the solid support and the substrate to which the solid support is adhered may be any known solid material such as metals; namely, aluminum, silver, copper, iron and their alloys, porous materials; namely, paper, wood, leather and fabrics, organic polymeric materials; namely, polyolefins including polyethylene and polypropylene, fluorocarbon polymers such as polytetrafluoroethylene and polyvinylfluoride, silicone elastomers and resins, polystyrene, polyamides such as Nylon, polyimides, polyesters and acrylic polymers, painted surfaces, siliceous materials such as concrete, bricks, cinderblocks and glass such as glass cloth. Porous materials such as glass cloth are often impregnated with a substance that will prevent the migration of the silicone pressure sensitive adhesive from one surface to another surface of the support. In this regard, it is also well known to chemically treat, physically treat (for example, etching) or primecoat (adding a curable polysiloxane) the surface of a substrate prior to addition of the silicone pressure sensitive adhesive compositions to enhance adhesion to said surface. Our invention is particularly suited to applications wherein good adhesion to a low energy surface (e.g., polyethylene or Teflon™) is desired.

[0045] The amount of silicone pressure sensitive adhesive composition applied to the surfaces is sufficient to render the surface tacky to the touch after the removal of any solvent having a boiling point of less than 200°C. After applying it to the surface, the adhesive is cured by air drying or heating at temperatures of up to 300°C.

[0046] Solid supports bearing the cured compositions of our invention are readily adhered to any solid substrate because the silicone pressure sensitive adhesive compositions of this invention have high tack and good adhesive strength.

[0047] Useful articles which are prepared with the silicone pressure sensitive adhesive compositions of this invention include pressure sensitive tapes, labels, emblems and other decorative or informational signs. In particular, our silicone pressure sensitive adhesive compositions are useful in tapes such as a splicing tape in label and paper stock manufacture and converting. An especially useful article is one comprising a flexible or rigid support that withstands extreme temperatures, hot and/or cold, and carrying on at least one surface thereof the silicone pressure sensitive adhesive compositions of our invention. Such an article makes full use of the stability at high temperatures and the flexibility at low temperatures that the silicone pressure sensitive adhesive compositions of this invention possess.

[0048] All parts and percentages are on a weight basis and all measurements were obtained at 25°C. unless otherwise indicated. The molecular weight properties of the polydimethylsiloxane polymers below were determined by Gas Phase Chromatography (GPC) in a toluene solvent, and using a polydimethylsiloxane standard.

[0049] The apparatus and testing procedures used for the results shown herein are as follows:

[0050] Adhesion was measured by applying a 6 x 1 inch strip of a Kapton™- or Mylar™-backed adhesive to a clean 2 x 6 inch stainless steel panel using two passes of a 4.5 lb. rubber-coated roller. The force required to remove the tape from the panel was measured with a Keil Tester at an peel angle of 180° at a rate of 12 inches per minute. The values recorded are the average of multiple readings taken during the course of one pull per sample. The Keil Tester is described in TAPPI, vol. 43, No. 8., pages 164A and 165A (August 1960). The readings are reported in units of ounces per inch (oz/in), as specified in said article.

[0051] Tack was measured on at least five 2.54 cm squares of the Kapton™ or Mylar™-backed adhesive using a POLYKEN^(R) probe tack tester, available from Testing Machines, Inc., Amityville, NY. The tack tester has a 0.5 cm diameter stainless steel probe. The test procedure used a 20 gram weight, a dwell time of 1.0 second and a pull speed of 0.5 cm per second. The results reported represent the average of at least five readings, expressed in g/cm².

[0052] Non-volatile content, i.e. percent solids, of an adhesive material was determined by heating a two g sample of the material at 150°C. for one hour and expressing the weight of the residue as a percentage of the original sample weight.

[0053] The non-volatile content of the MQ resins was determined by mixing 1.5 g of resin solution with 0.75 g of a polydimethylsiloxane fluid having a viscosity of 100 centistokes (cS) (100 mm²/s), followed by devolatilization at 150°C. for 2 hours.

[0054] The resins in the examples were analyzed using ²⁹Si NMR to determine the molar ratios of the (CH₃)₃SiO_1/2 units (M) to SiO_4/2 units (Q) in each resin and to determine the hydroxyl content of each resin.

[0055] Viscosities of the pressure sensitive adhesive compositions were measured in centipoise (cP) (1 cP = 1 millipascal-second (mPa·s)) at room temperature (25°+/-2°C.) using a Brookfield rotating disc viscometer fitted with an LV-4 spindle. Kinematic viscosities of starting polydimethylsiloxane fluids were recorded in centistokes (cS) (1 cS = 1 mm²/s).

[0056] The following materials were employed in preparing the compositions in the examples:

POLYMER A was a hydroxyl-endblocked polydimethylsiloxane fluid having a viscosity of 15,000 mm²/s, a number average molecular weight (Mn) of 38,200, and a weight average molecular weight (Mw) of 68,470.

RESIN A was a benzene-soluble, siloxane resin consisting of (CH₃)₃SiO_1/2 (M) units and SiO_4/2 (Q) units and having an M:Q molar ratio of 0.78:1.0, a hydroxyl content of 2.9 wt%, and the following molecular weight characteristics as determined by GPC in chloroform, using fractionated MQ resin standards and an IR detector, a Mn of 4,300, a Mw of 14,600, and a Mw/Mn of 3.395.

THERMAL STABILITY ADDITIVE was Ten-Cem® (a dispersion of a neodecanoate salt of a rare earth metal in mineral spirits having 6% active metals in the mineral spirits from Mooney Chemicals, Inc., Cleveland, Ohio).

PEROXIDES:

Perkadox(R) PD-50S-ps-a - a suspension of 50 wt% 2,4-dichlorobenzoyl peroxide in a proprietary polysiloxane fluid supplied by Akzo Chemical.

Benzoyl peroxide, in granular form, was 98% pure supplied by Aldrich Chemical Company.

EXAMPLE 1

[0057] First 150.1 g of Resin A, 73.6 g of polymer A, 58.3 g of toluene, 18 g of nonanoic acid and 0.06 g of a thermal stability additive, were combined and thoroughly blended in a three-necked flask equipped with a stirrer, thermometer, condenser and Dean Stark Trap. This mixture was heated to reflux, and maintained at reflux, for 4 hours. Water was continuously removed during the reflux step. The reaction product was then stripped at atmospheric pressure to 87% solids, cooled, recovered and stored for evaluation.

[0058] A portion of the product was catalyzed with Perkadox® PD-50S-ps-a at a level of 2 wt% peroxide solids based on solids. The catalyzed mixture was cast onto 50.8 µm polyester film (Mylar® A), de-volatilized for 2 minutes at 70°C., and finally cured for an additional 2 minutes at 178°C. The thickness of the film was 48.3 µm. The Probe Tack and 180 degree Peel Adhesion were then measured as described above. The silicone pressure sensitive adhesive composition had a Peel Adhesion of 42 oz/in and a Probe Tack of 1,089 g/cm².

EXAMPLE 2

[0059] Then 150.1 g of Resin A, 73.6 g of polymer A, 58.3 g of toluene, 18.0 g of Armeen®DM12D (dimethyldodecylamine from Akzo Nobel Chemicals, Inc., McCook, Ill.), and 0.06 g of a thermal stability additive, were combined and thoroughly blended in a three-necked flask equipped with a stirrer, thermometer, condenser and Dean Stark Trap. The mixture was heated to reflux, and maintained at reflux, for 4 hours. Water was continuously removed during the reflux step. The reaction product (adhesive) was then stripped at atmospheric pressure to 87% solids.

[0060] A portion of the adhesive was catalyzed with Perkadox® PD-50S-ps-a at a level of 2 wt% peroxide solids based on solids. The catalyzed mixture was cast onto 50.8 µm polyester film ( Mylar® A), de-volatilized for 2 minutes at 70°C., and finally cured for an additional 2 minutes at 178°C. The thickness of the film was 50.8 µm. The probe Tack and 180 degree Peel Adhesion were then measured as described above. The Peel Adhesion of this silicone pressure sensitive adhesive composition was >72 oz/in, and the Probe Tack was 1,381 g/cm².

EXAMPLE 3

[0061] Next 150.1 g of Resin A, 73.6 g of polymer A, 58.3 g of toluene, 7.8 g of Armeen® DM12D, 10.2 g oleic acid, and 0.06 g of a thermal stability additive, were combined and thoroughly blended in a three-necked flask equipped with a stirrer, thermometer, condenser and Dean Stark Trap. The mixture was heated to reflux, and maintained at reflux, for 4 hours. Water was continuously removed during the reflux step. The reaction product (adhesive) was then stripped at atmospheric pressure to 73% solids.

[0062] A portion of the adhesive was catalyzed with Perkadox® PD-50S-ps-a at a level of 2 wt% peroxide solids based on PSA solids. The catalyzed mixture was cast onto 50.8 µm polyester film (Mylar® A), de-volatilized for 2 minutes at 70°C., and finally cured for an additional 2 minutes at 178°C. The thickness of the film was 45.7 µm. The probe Tack and 180 degree Peel Adhesion were then measured as described above. The Peel Adhesion of this silicone pressure sensitive adhesive composition was >72 oz/in and the Probe Tack was 1,241 g/cm².

Claims

1. A silicone pressure sensitive adhesive composition obtainable by a method comprising the steps of

(I) reacting a mixture comprising:

(A)(i) at least one hydroxyl-terminated polydiorganosiloxane having a viscosity of from 100 to 100,000,000 mm²/s at 25°C. or (ii) a mixture of (a) a hydroxyl-terminated polydiorganosiloxane and (b) a polydiorganosiloxane selected from (i) polydiorganosiloxanes terminated with monovalent hydrocarbon radicals free of aliphatic unsaturation or (ii) alkenyl-terminated polydiorganosiloxanes wherein said mixture has a viscosity of from 100 to 100,000,000 mm²/s at 25°C;

(B) at least one soluble silicone resin consisting of at least one R₃SiO_1/2 unit and at least one SiO_4/2 unit, wherein R is independently selected from a monovalent hydrocarbon or halohydrocarbon radical free of aliphatic unsaturation and having from 1 to 20 carbon atoms, an alkenyl radical or a hydroxyl radical wherein the molar ratio of R₃SiO_1/2 units to SiO_4/2 units is from 0.5:1 to 1.2:1; and

(C) at least one solvent or plasticizer selected carboxylic acids having at least six carbon atoms and having a boiling point of at least 200°C. or amines having at least 9 carbon atoms and having a boiling point of at least 200°C. to form a reaction product; and

(II) adding (D) an organic peroxide or azo compound to the reaction product of (I).

2. The composition of claim 1 wherein the hydroxyl-terminated polydiorganosiloxane is a polydiorganosiloxane having the general formula

        HOR¹₂SiO(R¹₂SiO)_aSiR¹₂OH

wherein each R¹ is independently selected from a monovalent hydrocarbon or halohydrocarbon radical having from 1 to 20 carbon atoms or an alkenyl radical and

a" has a value such that the viscosity of said polydiorganosiloxane ranges from 1,000 to 500,000 mm²/s when measured at 25°C.

3. The composition of claim 1 wherein R is independently selected from methyl, phenyl, vinyl or hydroxyl, the molar ratio of R₃SiO_1/2 units to SiO_4/2 units is from 0.6:1 to 1:1, and (B) has a number average molecular weight of 3,000 to 7,500.

4. The composition of claim 1 wherein (C) is a carboxylic acid having at least six carbon atoms and having a boiling point of at least 200°C.

5. The composition of claim 1 wherein (C) is an amine having at least 9 carbon atoms and having a boiling point of at least 200°C.

6. The composition of claim 1 wherein (C) is a combination of a carboxylic acid having at least six carbon atoms and having a boiling point of at least 200°C. and an amine having at least 9 carbon atoms and having a boiling point of at least 200°C.

7. The composition of claim 1 wherein the mixture of step (I) further comprises (E) at least one solvent or plasticizer having a boiling point of at least 200°C. selected from the group consisting of aliphatic hydrocarbons, glycol ethers, esters, alcohols, ester alcohols, ketones, kerosenes, naphthas and petrolatums.

8. The composition of claim 1 wherein the mixture of step (I) further comprises a rare earth metal salt of a fatty acid.

9. The composition of claim 1 wherein the mixture of step (I) further comprises a solvent having a boiling point of less than 200°C.

10. The composition of claim 1 wherein (D) is selected from the group consisting of benzoyl peroxide, dichlorobenzoyl peroxide, 2,4-dimethyl-4-methoxyvaleronitrile and azobisisobutyronitrile.

11. The composition of claim 1 wherein the reaction product of step (I) has a solids content of at least 60% and a viscosity of up to 200,000 millipascal-seconds (mPa·s).

12. An article of manufacture obtainable by a method comprising

(I) applying a silicone pressure sensitive adhesive composition to at least one surface of a substrate, wherein the silicone pressure sensitive adhesive composition is obtainable by the method of any of claims 1 - 11 and

(II) heating the silicone pressure sensitive adhesive composition and the substrate to cure the composition.

13. The article of manufacture of claim 12 wherein the article is further obtained by (III) contacting a solid support with the substrate having the adhesive composition cured thereon after step (II) whereby the solid support and the substrate are adhered together.